Stripper Solution and Method of Manufacturing Liquid Crystal Display Using the Same

ABSTRACT

A method for manufacturing a liquid crystal display includes simultaneously forming a gate electrode and a gate bus line on a transparent dielectric substrate, simultaneously forming a channel layer, an ohmic contact layer, and source/drain electrodes by forming a gate insulation film, an amorphous silicon film, a doped amorphous silicon film, and a metal film on the transparent dielectric substrate on which the gate electrode and the gate bus line are formed and etching the metal film, the amorphous silicon film, and the doped amorphous silicon film, and forming a pixel electrode by forming a protective film and a transparent metal film on the transparent dielectric substrate upon which the source/drain electrodes are formed and finely etching the transparent metal film through a lift-off process using a stripper solution.

This application is a Divisional of Copending U.S. patent applicationSer. No. 12/837,313, filed Jul. 15, 2010, which is a Divisional of U.S.patent application Ser. No. 11/117,306, now U.S. Pat. No. 7,776,668, andclaims priority of Korean Patent Application No. 30206/2004 filed inKorea on Apr. 29, 2004, all of which are hereby incorporated byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD), andmore particularly, to a stripper solution to prevent yield degradationdue to particles produced during the LCD manufacturing process and amethod for manufacturing a LCD using the same.

2. Discussion of the Related Art

With the rapid change in the information society, one of the informationdisplay device, a LCD module, gained its popularity because of thegreater advantages, for example, miniaturization, lightweight, flatness,and low power consumption, as compared to a cathode ray tube (CRT). TheCRT has advantages in its performance and price, however, size andportability of the CRT are not matched up with the LCD. While the LCD isactively replacing the CRT with its advantages, however, LCD is moreexpensive than the CRT.

The LCD includes an array substrate on which a thin film transistor(TFT) is arranged, and includes a color filter substrate on which R/G/Bcolor filter layers are formed. The array substrate and the color filtersubstrate are pressed together with a liquid crystal layer interposedtherebetween. The array substrate and the color filter substrate aremanufactured through several mask processes. Specifically, the arraysubstrate is manufactured through a 5-mask process.

A first mask process includes forming a gate bus line and a gateelectrode on a transparent glass substrate by depositing a metal film onthe transparent glass substrate, thereafter etching the deposited metalfilm. Subsequently, a second mask process includes forming a channellayer on the substrate by forming a gate insulating film, an amorphoussilicon film, and a doped amorphous silicon film. Next, a third maskprocess includes forming source/drain electrodes and a data bus line bydepositing source/drain metal films on the substrate having the channellayer formed thereon and then etching the deposited source/drain metalfilms. Then, a fourth mask process includes forming a protective filmfor device protection and then forming a contact hole. Finally, a fifthmask process includes forming a pixel electrode by depositing an indiumtin oxide (ITO) transparent metal film on the substrate having theprotective film formed thereon and then etching deposited ITOtransparent metal film.

However, an increase in the total number of mask processes increases theLCD unit price. Accordingly, research for reducing the total number ofmask processes has been conducted. As a result, a 4-mask process wherethe channel layer and the source/drain electrodes are simultaneousformed has been developed.

FIG. 1 is a plan view illustrating a pixel structure of a related artLCD. Referring to FIG. 1, a gate bus line 1 for applying a drivingsignal and a data bus line 3 for applying a data signal are verticallyintersecting each other, whereby a unit pixel area is defined. A pixelelectrode 9 is disposed in the unit pixel area. A TFT, acting as, aswitching device is disposed on a region where the gate bus line 1 andthe data bus line 3 intersect each other vertically. The TFT includes agate electrode 5 electrically connected to the gate bus line 1, achannel layer formed on the gate electrode 5, and source/drainelectrodes 7 a and 7 b. When the TFT is turned ON, a data signal fromthe data line 3 is applied through the source electrode 7 a and thedrain electrode 7 b to the pixel electrode 9.

The data signal applied to the pixel electrode 9 forms an electric fieldin association with a common electrode, which rotates liquid crystalmolecules in a liquid crystal layer to adjust the transmissivity oflight passing through the liquid crystal layer. The adjusted lightpasses through the color filter layers of the color filter substrate,such that an image of various colors is displayed.

FIGS. 2A to 2D are cross-sectional views along line I-I′ of FIG. 1,illustrating a related art LCD manufacturing process of FIG. 1.

Referring to FIG. 2A, a metal film of Al or Cr is deposited on atransparent dielectric substrate 10 through a sputtering method.Accordingly, the gate bus line 1 and the gate electrode 5 are formedthrough a first mask process.

Referring to FIG. 2B, a gate insulating film 2 is formed on thedielectric substrate 10 and the gate electrode 5, thereafter anamorphous silicon film and an n+amorphous silicon film are formed. Then,a metal film is deposited on the dielectric substrate 10 on which the n+amorphous silicon film has been formed. Thereafter, the source/drainelectrodes 7 a and 7 b, an ohmic contact layer 6, and a channel layer 4are simultaneous formed through a second mask process by patterning ahalftone photoresist film, and successively etching the metal film, theamorphous silicon film, and the n+ amorphous silicon film. The halftonephotoresist film is patterned by using a diffractive exposure mask.

Referring to FIG. 2C, a protective film 11 is formed on a surface of thedielectric substrate 10 on which the source/drain electrodes 7 a and 7 bhave been formed. Then, a contact hole is formed exposing the drainelectrode 7B through a second mask process.

Referring to FIG. 2D, a transparent ITO metal film is deposited on thedielectric substrate 10 on which the contact hole has been formed. Then,the pixel electrode 9 is formed through a fourth mask process tocomplete the LCD manufacturing process. However, when compared with a3-mask process that is being developed, the 4-mask process increases theLCD manufacturing cost because of the increased total number ofindividual mask processes.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a stripper solutionand a method for manufacturing a LCD using the same that substantiallyobviate one or more of the problems due to limitations and disadvantagesof the related art.

An object of the present invention is to provide a stripper solution toprevent yield degradation due to particles produced during the LCDmanufacturing process and a method for manufacturing a LCD using thesame.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will become apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a methodfor manufacturing a liquid crystal display includes simultaneouslyforming a gate electrode and a gate bus line on a transparent dielectricsubstrate, simultaneously forming a channel layer, an ohmic contactlayer, and source/drain electrodes by forming a gate insulation film, anamorphous silicon film, a doped amorphous silicon film, and a metal filmon the transparent dielectric substrate on which the gate electrode andthe gate bus line are formed and etching the metal film, the amorphoussilicon film, and the doped amorphous silicon film, and forming a pixelelectrode by forming a protective film and a transparent metal film onthe transparent dielectric substrate upon which the source/drainelectrodes are formed and finely etching the transparent metal filmthrough a lift-off process using a stripper solution.

In another aspect, a method of etching a transparent metal film includessubjecting the transparent conducting film to a stripper solution, andsubjecting a photoresist film disposed beneath the transparent metalfilm to the stripper solution, wherein the stripper solution finelyetches a surface of the transparent metal film and removes thephotoresist film.

In another aspect, a method for manufacturing a liquid crystal displayincludes forming a gate electrode and a gate bus line on a transparentdielectric substrate, forming a gate insulation film, an amorphoussilicon film, a doped amorphous silicon film, and a metal film on thetransparent dielectric substrate, and etching the metal film, theamorphous silicon film, and the doped amorphous silicon film, forming aprotective film on the transparent dielectric substrate, forming aphotoresist film on the protective film, patterning the photoresistfilm, etching the protective film using the patterned photoresist film,forming a transparent metal film on the transparent dielectricsubstrate, the transparent metal film including a first portion disposedon the patterned photoresist film and a second portion disposed on thetransparent dielectric substrate, and removing the photoresist film andthe first portion of the transparent metal film using a lift-off processincluding a stripper solution, wherein the stripper solution finelyetches particles of the transparent metal film produced during thelift-off process.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a plan view illustrating a pixel structure of a related artLCD;

FIGS. 2A to 2D are cross-sectional views along I-I′ of FIG. 1,illustrating a LCD manufacturing process of FIG. 1;

FIGS. 3A to 3E are cross-sectional views illustrating an exemplaryprocess for manufacturing an LCD according to the present invention; and

FIGS. 4A to 4D illustrate an exemplary state where an ITO metal film isfinely etched with a stripper solution according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIGS. 3A to 3E are cross-sectional views illustrating an exemplaryprocess for manufacturing an LCD according to the present invention.Referring to FIG. 3A, a metal film is deposited on a transparentdielectric substrate 100 through a sputtering method. Then, a gate busline and a gate electrode 105 are formed by etching the metal filmthrough a first mask process.

Referring to FIG. 3B, a gate insulating film 102 is formed on thedielectric substrate 100 on which the gate electrode 105 has beenformed, and then an amorphous silicon film and an n+ amorphous siliconfilm are formed. A metal film is deposited on the dielectric substrate100 on which the n+ amorphous silicon film has been formed. Then,source/drain electrodes 107 a and 107 b, an ohmic contact layer 106, anda channel layer 104 are simultaneously formed by etching the metal film,the amorphous silicon film, and the n+ amorphous silicon film using ahalftone patterned photoresist film. The halftone photoresist film ispatterned through a diffractive exposure process by a second maskprocess.

Referring to FIG. 3C, a protective film 111 is formed on a surface ofthe dielectric substrate 100 on which the source/drain electrodes 107 aand 107 b have been formed. Then, the protective film 111 is etched bypatterning a photoresist film 150. At this time, the protective film 111formed in the pixel area is completely removed and thus the dielectricsubstrate 100 is exposed to the outside.

Referring to FIG. 3D, a transparent metal film 115 of ITO metal orindium zinc oxide (IZO) metal is deposited on the whole area of thedielectric substrate 100 on which the photoresist film 150 is patterned.Since the patterned photoresist film 150 exists on a region where thegate electrode 105 and the source/drain electrodes 107 a and 107 b areformed, the transparent metal film 115 is deposited on the patternedphotoresist film 150 and the dielectric substrate 100. After thetransparent metal film 115 is deposited, the patterned photoresist film150 is removed through a lift-off process.

When the transparent metal film 115 formed on the patterned photoresistfilm 150 is removed through the lift-off process, ITO or IZO transparentmetal breaks into particles in the stripper solution. Since the strippersolution is repeatedly used in the LCD manufacturing process, the amountof particles in the stripper solution gradually increases. Accordingly,the accumulation of the ITO or IZO transparent metal particles causeserrors.

Accordingly, in the present invention, thiobenzoic acid or sulfonic acid(i.e., a carboxyl group) of 2 wt % is included in the stripper solution.Thus, the transparent metal particles can be removed from the strippersolution, such that particles of transparent metal film 115 and thepatterned photoresist film 150 are simultaneously removed with astripper solution through a fine etching process. In addition, theaccumulation of the particles in the stripper solution is prevented byetching the particles finely. Thus, the stripper solution having lowparticle content can be used during repetitive lift-off processes,thereby increases yield of the LCD.

The content of the thiobenzoic acid or the sulfonic acid in the strippersolution is not limited to 2 wt %, but may be adjusted within a rangethat enables a fine etching of the transparent particles withoutaffecting the pixel electrode formed through the lift-off process duringthe 3-mask process. In addition, the stripper solution may be formed ofan MEA, BDG or NMP base.

In the exemplary embodiment of the present invention, the transparentmetal particles are removed from the stripper solution through a fineetching process after 1-2 hours of the lift-off process. Thus, since thelift-off process completes within a relatively short time, the pixelelectrode is not damaged by the stripper solution during the lift-offprocess.

The transparent metal particles and the patterned photoresist film 150are removed together through a lift-off process using the strippersolution containing thiobenzoic acid or sulfonic acid. The transparentparticles that are removed are gradually etched, in addition to beingremoved from the stripper solution. Accordingly, the particle density inthe stripper solution is gradually reduced. The transparent metal film115 formed through the process of FIG. 3D is electrically connected toone side portion of the drain electrode 107 b.

FIG. 3E illustrates a process in which the photoresist film is removedand a pixel electrode 115 a is formed. As shown in FIG. 3E, the pixelelectrode 115 a is electrically connected to the drain electrode 107 bwhen manufactured through the lift-off process. In addition, the gateelectrode 105 and the pixel electrode 115 a are formed on the same planeupon an upper surface of the dielectric substrate 100. The fine etchingprocess using the stripper solution of the exemplary embodiment isperformed while the protective film 111 and the pixel electrode 115 aare simultaneously formed through the lift-off process during the thirdmask process. Accordingly, errors due to the accumulated particles inthe stripper solution during the LCD manufacturing process areminimized.

FIGS. 4A-4D illustrate an exemplary state where an ITO metal film (i.e.,the transparent metal film 115) is finely etched using the strippersolution of the exemplary embodiment, in which the stripper solutionincludes thiobenzoic acid by about 2 wt %. In detail, FIG. 4Aillustrates a state where the ITO metal film is divided through thelift-off process, FIG. 4B illustrates a state after 30 minutes from thestate shown in FIG. 4A, FIG. 4C illustrates a state after one hour fromthe state in FIG. 4A, and, FIG. 4D illustrates a state after two hoursfrom the state in FIG. 4A. States similar to those in FIGS. 4A through4D can be found in the case of the IZO metal film.

Referring to FIG. 4B, the ITO metal film starts to etch in the strippersolution after 30 minutes. The surface of the ITP metal film shows finesurface after two hours of etching. Unlike a wet etchant, the trippersolution (or solvent) of the exemplary embodiment gradually etches theITO metal film. In addition, the stripper solution of the exemplaryembodiment, which includes thiobenzoic acid or sulfonic acid, can removethe ITO or IZO particles therefrom while removing the photoresist filmduring the lift-off process. Accordingly, the stripper solution of theexemplary embodiment removes only the photoresist film during thelift-off process, and finely etches and removes the transparent metalparticles in a repeatedly-used stripper solution.

In FIGS. 4A-4D, the stripper solution, which is added with thethiobenzoic acid by about 2 wt %, is used to finely etch the ITO metalfilm (i.e., transparent metal film). The content of the addedthiobenzoic acid may be adjusted within a range that does not damage thepixel electrode formed on the substrate during the lift-off process.Accordingly, the thiobenzoic acid may be substituted by the sulfonicacid.

As described above, the exemplary embodiment of the present inventionfinely etches and removes ITO or IZO particles that accumulate in thestripper solution during repeated lift-off processes, thereby preventingthe LCD yield degradation due to the particles.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the stripper solution andmethod for manufacturing liquid crystal display using the same of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. A stripper solution comprising a predetermined content of a carboxyl group material including a thiobenzoic acid material.
 2. The stripper solution according to claim 1, wherein the predetermined content of the carboxyl group material is about 2 wt %. 